1. Field of the Invention
This invention relates to an apparatus and method for handling discrete relatively rigid or stiff sheets, and more particularly, to a system for conveying the sheets in a direction generally corresponding to the planes thereof while simultaneously applying suction forces to the sheets in a direction substantially normal to the planes thereof to lift the sheets away from a support surface.
2. Description of the Prior Art
The present invention has application to any operating environment wherein it is desired to serially convey discrete relatively rigid or stiff sheets quickly and in such a manner as to minimize physical contact between the sheet and a support surface. By minimizing frictional effects between the sheets and a support surface, the sheets may be fed at a faster rate than is possible with prior art systems. Further, removal of the conveyed sheet from a table or other support minimizes the possibility of jam-ups.
The most common form of sheet conveyors are mechanical systems, employing, for example, rope or belt conveyors to transport the sheets. Such mechanical conveyors, however, have a number of drawbacks. Not only are such mechanical arrangements subject to wear, they are also very limited as to performance. If operated at high production rates, the rope or belt conveyors often cannot maintain accuracy of sheet placement. Such mechanical arrangements are characterized by frictional forces being applied to the sheets during operation which, as stated above, provides limitations upon the rate of conveyance.
While air tables and similar arrangements are known and widely used in the conveying art, such prior art devices, which rely on a positive air pressure between the conveyed article and a support surface to operate, have built-in deficiencies. If too great an air pressure is applied to the article during conveyance in an attempt to provide a high degree of clearance between the support surface and the conveyed article, conveyance of the article may actually be interfered with due to a conflict between the propelling gaseous forces and the gaseous forces separating the articles from the support surface. This will result in a slow-down of the conveying process.
U.S. Pat. No. 4,453,709, issued to Imants Reba on June 12, 1984 discloses a system for conveying discrete flexible articles; however, such system is not appropriate for conveying relatively rigid or stiff articles, such as, for example, place mats.